Many industrial processes require the release of high-pressure fluids to the atmosphere. The high-pressure fluids released typically comprise steam and gases that are expelled through vent or blow down systems of steam turbines, steam piping systems, and natural gas storage and compressor stations. Vent systems are typically characterized by a relatively constant flow of pressurized gas whereas blowdown systems are characterized by the release of fixed volumes of gas. Vent and blowdown systems can range in diameter from only a few inches to many feet and may vary in length from a few feet to upwards of forty feet or more. In most cases, high-pressure fluid releases cause the formation of turbulent jet flow, which results in the formation of excessive noise levels that can exceed over 120 decibels (dB). In effect, the noise created by such high-pressure releases is equivalent to that created by the engines of jet airplanes.
The exposure to such excessive noise levels can result in permanent ear damage and/or permanent hearing loss. For this reason, laws, regulations and guidelines exist to protect individuals in the workplace and to protect those living near industrial settings from exposures to such high levels of noise. For instance, the Occupational Safety and Health Act (OSHA) of 1970 specifically relates to the occupational exposure of workers to excessive noise and the Noise Control Act of 1972 mandates the Environmental Protection Agency (EPA) establish noise limits that are protective of public health and welfare. In addition to federal regulatory efforts, various states and cities have enacted laws, regulations and guidelines that establish acceptable maximum noise levels acceptable at or near industrial settings. These levels typically vary according to whether an area is zoned as being heavy industrial, commercial, residential, etc. Hence, most industrial facilities in the United States include sound control and/or sound abatement devices to control noise levels.
Heretofore, control of most noise has been typically achieved by means of isolating the noise and/or dissipating noise after formation utilizing sound absorption materials, acoustic shields and barriers (fixed and movable), acoustic enclosures, or by the use of diffusers. Diffusers typically distribute the flow of fluids streams evenly through the inlet portion of a silencer and shift the noise to a frequency that can be attenuated by the remainder of the silencer assembly. Diffusers, thus, contribute little to the actual attenuation of the noise generated by the fluid stream. On the contrary, some diffusers comprising a series of closely spaced, nested and perforated pipes impart a tortuous path upon the flow of the fluid stream and provide some reduction in the levels of noise. However, the level of noise reduction provided by such diffusers is minimal.
Significant reductions in the level of noise produced in industrial settings can be achieved by preventing the very formation of turbulent jet fluid streams that produce excessive noise. Additionally, preventing the formation of turbulent fluid jet streams can be more cost effective as sound absorptive, attenuation and/or deflection devices may no longer be needed.
Additionally, many sound attenuation devices comprise acoustic pack materials that are not satisfactory for high temperature or high pressure applications. Moreover, many acoustic pack materials tend to migrate or break down within the device housing, which reduces the efficacy of the noise attenuation device.
What is needed then is a noise attenuation device for high pressure, high temperature fluid flow applications that comprises a pack material that is resistant to breakdown and migration and which prevents the initial formation of turbulent jet flow such that additional sound absorption, attenuation and/or deflection devices is not required.